THE SUSPECT: Detectives lead a ranting Erika Menendez from the 112th Precinct station house in Queens last night. A tip from someone who recognized her in Brooklyn led police to apprehend her. Photo: Michael Hicks

TRAGEDY: Busted suspect Erika Menendez allegedly told cops yesterday that hatred of Muslims over the 9/11 attacks led her to shove Sunando Sen — a Hindu — in front of a 7 train at this Queens station. Someone who answered the phone at her home said she’s bipolar. (Seth Gottfried)

The crazed woman who shoved a Queens immigrant to his gruesome death in front of a subway train told cops yesterday that she did so because she thought he was a Muslim, authorities said.

Erika Menendez, 31, was charged with second-degree murder as a hate crime after admitting to investigators that she pushed Sunando Sen, 46 — a Hindu — in front of a 7 train in Sunnyside on Thursday night, officials said.

She allegedly said she singled him out because of his religion.

“She is accused of committing a subway commuter’s worst nightmare — suddenly and senselessly pushed into the path of an oncoming train, shoved from behind with no chance to defend himself,” said Queens DA Richard Brown.

“She told police that she pushed a Muslim off the train tracks. She said, ‘I’ve hated Hindus and Muslims since 2001, since they put down the Twin Towers. I have been beating them up since.’ ”

There were no Hindus involved in the 9/11 attacks.

Menendez faces 25 years to life in prison if found guilty.

She looked wild as she was escorted from the 112th Precinct station house.

She wailed incoherently, contorted her face into what looked like a fiendish grin, and struggled as officers forced her into an unmarked car.

She appeared equally unhinged later during her arraignment hearing in Queens Criminal Court. Menendez was laughing so hard that she was visibly shaking as Assistant District Attorney Michelle Kaszuba read the charges against her.

“You’re going to have to have your client stop laughing,” Judge Gia Morris said, scolding Menendez’s lawyer. Despite this admonishment, Menendez laughed several more times at the hearing. She’ll undergo a psychiatric test today.

Menendez was nabbed after a Brooklyn tipster had called in after recognizing her on the street from surveillance video circulated by the NYPD, sources said.

Officers from the 71st Precinct busted her in Crown Heights after spotting her wearing the same jacket seen in a surveillance video recorded near the crime scene.

Menendez was picked up at about 5 a.m. on Empire Boulevard and Bedford Avenue, the sources said. She continued mumbling in coherently as investigators questioned her — and at one point asked where the R train was, the sources added.

She was interrogated yesterday at the same Forest Hills, Queens, station house. She initially denied being at the subway station at the time of the fatal push, telling cops she was smoking pot with a pal. She later admitted committing the attack, telling cops “I’ll just plead guilty,” a prosecutor said at the arraignment hearing.

In addition to the tip that led to her arrest, her brother also dropped a dime on her Friday night after seeing her on the news. But his tip played no role in her capture, according to law-enforcement sources.

A man who answered the phone at her family’s apartment said Menendez was a troubled woman.

“Erika is a bipolar person, and that is why this happened — not because she was a terrorist,” he said. “She’s been in Elmhurst Hospital 10 to 15 times.”

Her building’s doorman said she goes out of control when she goes off her meds.

“She would go off the wall sometimes in the house,” said Angel Luis Santiago. “[Her parents] called the cops on her to take her out of the house. When she don’t take her medication, she goes really wacky.”

She also had a parade of boyfriends, he said, explaining that “she would just pick one up here and drop another one off.”

One such boyfriend was barred from her building after he was found naked in a hallway, a tenant said.

“He was extremely high. He was found down in the hallway nude,” said the neighbor, Janet Henne. “He was not allowed back in the building.”

Relatives said they had tried repeatedly to get Menendez help.

“My sister has sought help for Erika when she’s gotten in trouble before and has never gotten any,” said her aunt. “When they go into the hospital, they just give her two pills and throw her back out on the street.”

Sen, who was from Calcutta and co-owned a Manhattan print shop, was waiting for the train at about 8 p.m. Thursday when Menendez came up from behind and shoved him to the tracks, the sources said.

His roommate, Akash Sarker, 20, yesterday said Sen was going home from the bank when the attack occurred.

Menendez, who alternated between sitting on the bench and pacing on the platform, was swearing to herself just before the attack, officials said.

She jumped from the bench and pushed him with both hands as the train came into the station, the sources said. Sen landed on the rail bed, where his head was crushed by the second car.

“I just pushed him in front of the train because I’d thought it’d be cool,” Menendez allegedly told investigators, calling the attack, “spontaneous.”

The doomed man desperately tried to climb back to the platform, but couldn’t get out of the way in time, a witness said.

Sen had recently started his business after suffering a stroke.

“He had a stroke a few months ago. He couldn’t work for a while,” Sarker said. “So we let him stay here. And then he opened his print shop.” The funeral is scheduled to be held in two weeks.

This was the city’s second fatal subway pushing this month. Ki Suk Han was shoved to his death, allegedly by drifter Naeem Davis, in Midtown.

“And if I do, I’m staying away from the platform. That’s for sure. It’s such a horrible way to die. This city can’t take any more of these kinds of crimes.”

Todd Lemieux, 24, a Queens College student, said, “I don’t know if it makes me feel safer. Seems like it’s happening more and more now.”